Manufacture of plasters



Patented Jan. 1 1935 MANUFACTURE oF'r'LAs'TERs I VictoriLef ebure, Hampstead, London," England I -'No "Drawing. I Application September 5,, 1930, Serial No.-479,931. Great BritainOctober 1i rn my UQS.AQPatentSpecificatiOn'No. 1,879,877

it is sli otvnf how natural fanhydrite, formerl; 1'3, waste material of no value for plaster making, canhe converted into 'a good plaster. Il'1a\ e now found foth er ways of making new" form s of anhydri'te plasters: whieh have 'distinct cdmn'iercaradvamages. i I V According to thisinventic in l provide a; process offiiianufacture "or anhydrite plasters 'whichconsists' in 'm'ixing 'z'agnhydrite"with thehemihydrated form-of calcium-sulphate, CaSO4 AzHzO, which is the standard chemicalcomposition df plasterpf Paris.

luted with fillers such as powdered silica or gy sum the mass-after 'settingj 'lieconies correspond ni'gly weak "and soft according to'-the amount of dilution, whieh 'resultfwould he expected" the dilution or demerits and binders withinerti fillers in general. 'But ifground anhydritefhe employed instead of fillerssuch as the above it id'o'snot act as a diluent but for a git en concentration gives a niuch harder and stronger mass.

The following example illustrates tion, the parts' beingfbyfvoluinel "Example-One part of plaster of'Par'isis mixed with'eight parts powderedsilica; theresuIting mass after settingwith water in the usualway, is very weak and soft, quite unusableas a plas-' ter. One part of the same plaster offParisand eight-parts ground anhi drite, after, treating'in theisanie manner with water, give a mass as hard and strong as the neat pla'ster swans,

Another important advantagejof the process of manufacture according to this invention is the increase inspeed offsetting; and improvement in properties of standard wallplastersby the additionwof anhydrite, or'of accelerated? anhydri'te. "By the latter I refer to su'chlanhydrit'e-plasters' as a're covered by the patent men s Claims. }(01. 106- 34) steward plasterysuch'-as-plaster of Paris- 9r b t w l-Knew i'lr e 10 qlld hard plasters, containing CaSOU/QHQO-be' "di the inven- In the industryorgamc fretardersf are used to m'ixture will set in'jfrom less than one minjutequp to' fifteenfminutes, much? quicker than eithero the components. For example, a mixture off on "part of mediums'etting hard wall plaster "with a-s'etfof ahout one liburg'miz ied 'wi'th s of aiihydrite pieaer arrangea toset about one hour will set to" a hard-'iriass'a-lmost n two or thr'ee minutes, varying w h "oofiditi ns such-as temperature andexce'ss' water; Although this observed efieet of speed-has been found true'ingenei'alin the adini x tiires" of anhyeme 61'" ae eeie'rate'd anhydrite with" hernihydrated plaste'rs t ere will be some forms of the latter in which" the increase of speed; although substantial r'i'iay not: beso great. f-For' example, in admixtures of aecelerated anhiidrite withKeehes' cemenu-wiiich isaetwneny-a hydratedplaster view 'of'itsdouble ahd l iigher' temperature roasting, the speed inayhe fredu'eed frdm' four hours *downto about 25-1rrlirnll'te's, but notnecessarilyfdownto-one minute, V

Thus 'the rfiethod can employed to i crease the setting speed o-f *slow wall plasters or; by heavy'lo' "ding withanhydriteyto reduoeith'e speed ulding -plasters, tln'is prGidlliiing' plas- I a1 or 'better duality thar'istandard t substantially ldwercbst, thematerm simply ground kminei alanhydr ite; or 'the latter with atrace o'i lbw -pjried batal yst. 'As an example, the standard liehti'hydrated g eammanat has aweryflli ck se 'm ms form it is' used formouldifig asifplajster br rris;

duce the-*spee'd. A ccordingg to'thisinvehtionyit is'poss'ihleto'reducethespeed, making plas; tel suitable for, van purposes ib'y. ad percentages of Hams/ante, such "as, for ex 9 mm bi ri ai t Pari 'lY e tr' rt a: anhydrite, ,I hayefoundthat thequicke st frnixtures, which are almost mstantaneous consist of one volume :of the; hemihydrated vform frgomaloout :one hali 'to three volumesof acceleratedsianhydrite. Atsomepomtsxbetweeni these proe portions, v arying'with' the raw materials; whereas a peak of speed.

The following table gives the variation of speed with admixture employinga standardcommercial retarded hemihydrated plaster and an accelerated anhydrite, both setting individually in about 60 minutes:

Percent Percent standard accelerated Setting time plaster anhydrite Minutes Nil. 100 60 10 90 16 20 80 4 40 60 2% 50 50 l 60 40 2% 80 20 5% 100 60 and the following table gives the variation employing the same standard plaster and non-accelerated anhydrite with a practically indefinite setting time:-

Percent Percent I nonstalralsdtaarrd accelerated Setting time p anhydrite 3 Nil. 100 No practical set. 10 90 15 minutes. 20 80 6 minutes. 40 v 60 6 minutes. 80 20 24 minutes. 100 Nil. 60 minutes.

The slowest mixtures are obtained by heavy dilution with the unaccelerated anhydrite. This gives a very satisfactory and easily standardized method of controlling speed of set without the addition of undesirable organic substances, or without loading with high percentages of inorganic accelerators.

These mixtures have various other advantages besides those mentioned above: First, the set mass from the mixture when using the accelerated anhydrite, is as hard and strong as (in fact,almost invariably harder and stronger than) the normal hemihydrated plaster in the mixture when used alone. In using high percentages of non-accelerated anhydrite the resultant set'mass is not always harder and stronger, but makes as good practical plaster up to very high dilution. Secondly, the anhydrite content of the mixture im: proves the final product in the direction of the properties of anhydrite plasters, not only as regards hardness and strength, but as regards a surface more suitable for rapid after decoration. Thirdly, the normal methodof producing very rapid anhydrite plasters is to increase the setting or accelerating agent percentage, which increases cost. The mixtures according to the present invention, enable-very fast plasters up to a practically instantaneous set, to be made at lower cost, employing in the combinationeither anhydrite alone or anhydrite with very small percentages of setting agent. Another advantage which has been observed is that for practical use mixtures can be obtained which have a higher sandcarrying capacity than the two components, certainly as regards the initial strength of the mass as distinguished from the ultimate strength, which is a point of considerable practical importance.

The manner in which the invention is applicable to various requirements is further illustrated by the following examples, which are by no means limitative of the field of usefulness of the invention.

Example 1 .--WaZZ plaster A plaster suitable for wall surfaces in normal building operations made by the mixture of one part of standard retarded hemihydrated plaster, having afirm set of about 60 minutes, with 9 parts of anhydrite containing 0.2% of potassium sulphate and zinc sulphate salts in molecular proportions, having itself a firm set of about hours. This resultant mixed wall plaster has a firm set of about60 minutes, being of average speed for wall work.

Example 2.,Casting or-moulding plaster A plaster suitable for very quick work, made by mixing one part by volume of a standard retarded hemihydrated plaster with 4 parts by volume of anhydrite containing 2% of potassium sulphate and zinc sulphate mixed salts in molecular proportions.

What I claim and desire to secure by Letters Patent is:- v

1. A plaster composition consisting of two components only in which the first component consists of unburnt natural anhydrite (CaSO4), and the second component consists of burnt gypsum (CaSO4. /2I'I2O), in the proportions of 1-9 parts of the first component to 1 part of the second.

2. A plaster composition consisting of two components only in which the first component consists of accelerated unburnt natural anhydrite (CaSOr), and the second component consists of burnt gypsum (CaSO4. /2H2O).

3. A plaster composition consisting of two components only in which the first component consists of unburnt natural anhydrite (CaSOq), and the second component consists of a retarded CaSOl. /2H2O wall plaster.

4. A plaster composition consisting of two components only in which the first component consists of accelerated unburnt natural anhydrite (C3804) and the second component consists of a retarded CaSO4. /2HzO wall plaster.

5. A plaster composition consisting of two components only in which the first component consists of accelerated unburnt natural anhydrite (C3804), and the second component consists of a retarded CaSOM/ I-IzO wall plaster.

6; A plaster composition consisting of two components only having a firm set of about 1 hour,

in whichthe first component consists of unburnt natural anhydrite containing about 0.2% of potassium sulphate and zinc sulphate in molecular proportions, having a firm set of about 5 hours,

and the second component consists of a retarded CLsO4. /gH2O wall plaster having a firm set of about 1 hour.

VICTOR LEFEBURE. 

